This application relates to a refrigerant system wherein an engine, such as an internal combustion engine, is utilized to provide power to mobile air conditioning equipment, and wherein a pulse width modulation control for the engine is provided to allow variation in the refrigerant system capacity.
Refrigerant systems are utilized to condition a secondary fluid, such as air. One class of refrigerant system applications is related to mobile air conditioning or refrigeration equipment. This class of mobile applications includes portable chillers, portable packaged systems, mobile container refrigeration units, transport tractor-trailer or truck refrigeration systems, etc. Components for the refrigerant system, such as compressors, fans and pumps are typically driven by an engine power source, using clutches, belts, couplings and other similar components.
The requirements on the cooling (or heating) capacity to be delivered to the conditioned spaces vary, for example, due to internal load within the conditioned environment as well as ambient conditions. In the past, various techniques for component unloading or decreasing the capacity of the refrigerant system have been utilized for mobile air conditioning and refrigeration equipment. One of such techniques included operation of the engine at two discrete speeds. When lower capacity was required, the engine was operating at a lower speed, and when a higher capacity was required, the engine was operating at a higher speed. Since the engine was coupled to a compressor, when the engine speed was reduced the compressor speed would also be reduced proportionally. As the compressor was operating at a lower speed, it would be delivering less refrigerant circulating throughout a refrigerant system and subsequently provide lower capacity to the environment to be conditioned. However, in this case, the capacity of the system could only vary in two digitized increments corresponding to at a high or low speed of continuous operation. When the engine cycles from a high to low speed, it would operate at a particular speed for a long period of time (typically from 10 minutes to several hours). Since the engine and the compressor would stay at a given speed for such a long period of time, the temperature of the conditioned environment could not be precisely controlled. Thus, other means (often very expensive and inefficient) for fine-tuning the delivered capacity were required. These means, for example, included the use of a suction modulation valve. When a reduced capacity is desired, the opening through the suction modulation valve is decreased, causing the reduction of refrigerant delivered to the compressor. While effective in terms of capacity reduction, this technique results in inefficient operation requiring extra undesirable fuel consumption and decreased refueling intervals. Thus, the need exists to improve engine fuel consumption while maintaining tight temperature control in the conditioned environment.
It is also known to provide pulse width modulation control for various components in a refrigerant system to control delivered capacity. In one known type of pulse width modulation control, a system control rapidly cycles a suction valve between open and closed positions to control the amount of refrigerant delivered to a compressor. In this manner, as known, the capacity provided by the refrigerant system would be reduced. This technique, while applied to a suction valve, has not been utilized or adapted to rapidly cycle between the speeds of the multi-speed engine driving the refrigerant system components.